This invention relates to control systems for work-performing vehicles such as lift trucks, front end loaders, or the like, wherein the vehicle may move across the underlying terrain and wherein the same includes a load handling device or the like relatively movable on the vehicle frame. Typically, but not always, the load handling device will undergo compound movement relative to the vehicle frame.
Prior art of possible relevance includes commonly assigned U.S. Pat. No. 3,983,462, issued Sept. 28, 1976 to Jones; commonly assigned U.S. Pat. No. 4,093,091 issued June 6, 1978 (now U.S. Pat. No. 4,093,091), entitled "Load Moment Sensing System For Lift Trucks", in the name of Gregg et al; and United Kingdom specification No. 1,385,099 to Coventry Climax Engines Ltd., published Feb. 6, 1975.
Lift trucks and front end loaders have greatly increased in popularity due to their maneuvering ability and load carrying capacity. As is well known, such vehicles include lift arms or a mast on the front end of the vehicle which carry a load handling means. In the case of lift trucks, the mast is pivoted to the vehicle and a carriage in the form of a fork or the like is mounted for reciprocatory movement on the mast. In the case of front end loaders, buckets typically are pivoted on the lift arms and are movable with respect thereto.
Because the load is carried forwardly of the center of gravity of the vehicle, increased loading on the carriage or bucket increases the tendency of the vehicle to become overloaded in its forward direction.
Various means have been provided for warning the operator of such a vehicle of an overload condition and/or for varying the operation of the vehicle to preclude an overload condition from occurring. For example, in the system of the above-identified Gregg et al application, when a predetermined overload condition is sensed, certain functions are disabled, preventing the intensification of the overload condition. In other cases, when the predetermined overload condition is sensed, an audible or visual warning will be adduced at the time to warn the operator that the overload condition should not be intensified.
The Gregg et al system works extremely well for its intended purpose in preventing an overload condition from occurring. However, since it shuts down certain of the functions of the vehicle when an overload condition is sensed, it is necessary that the overload condition first be relieved before full use of the vehicle may be resumed.
In the case of those systems providing only an audible or visual warning, such occur only at the time the overload condition is detected and if the vehicles are being controlled by an unmindful operator, the overload condition may be aggravated.